(1) Field of the Invention
This invention relates to an automatic transmission for use in an automotive vehicle, and more particularly to an automatic transmission having an overdrive gear mechanism positioned between a hydrokinetic torque converter and an underdrive.
(2) Description of the Prior Art
As is well known, an automatic transmission for automotive vehicles operates to automatically change gear reduction ratios in response to vehicle speed and load on the vehicle engine. An automatic transmission in general consists of a torque converter and an underdrive gear mechanism which is coupled to the converter and establishes two or more gear reduction ratios of no less than 1. Recently, a demand has arisen for an automatic transmission with overdrive in order to improve engine efficiency and emission control of the engine.
It has been common practice, when an overdrive gear mechanism is to be added to an automatic transmisson, to position the overdrive gear mechanism on the output side of the automatic transmission. This is to enable ease of design change in the automatic transmission itself.
However, in a situation where an overdrive gear mechanism is built into the transmission itself in the rear part thereof, torque from the engine is increased by the underdrive gear mechanism and is transmitted to the overdrive gear mechanism. Thus, the strength of the gears provided must be substantially increased, and an excessive increase in the amount of anti-friction materials provided is also required.
Accordingly problems arise with regard to durability and cost, with an accompanying increase in the size of the transmission. In addition, when the automatic transmission thus arranged is installed on a vehicle, considerable design changes are required for the vehicle body.
It is accordingly an aim of the present invention to provide an automatic transmission with overdrive, which avoids the aforementioned shortcomings by positioning the overdrive gear mechanism between a hydrokinetic torque converter and an underdrive gear mechanism of the assembly i.e., on the input side of the underdrive gear mechanism.
The invention is intended to provide an automatic transmission which require little or no design change not only on the side of the vehicle body but also on the side of a conventional type automatic transmission itself.
Furthermore, the invention is directed to an automatic transmission with overdrive, which is compact in size and well accommodated to mass production.
More specifically, the invention is directed towards an automatic transmission with overdrive, which includes a torque converter segment, an overdrive segment and an underdrive segment, which are provided separately of each other and which may be assembled or fastened together with only simple fastening means, thereby allowing desired interchangeability and simple assembly.
The invention is intended to enable utilization of conventional components, such as planetary gears, one-way clutches, and frictional engaging means, of the type normally in use in an overdrive gear mechanism, thereby establishing standerization of parts.